Electrical control device



1949 J. c. BARNES EIAL ELECTRICAL CONTROL DEVICE Filed Aug. 30, 1946 INVENTORS .dEAN C. BARNES AND BY 112A hPENNIMAN -6- MW ATTORNEYS Patented Dec. 27, 1949 ELECTRICAL CONTROL DEVICE Jean C. Barnes, Massillon, and Ira B. Penniman, Canton, Ohio, assignors to The Weber Dental Manufacturing 00., Canton, Ohio, a corporation of Ohio Application August 30, 1946, Serial No. 693,912

4 Claims. 1

This invention relates to electric motor speed control, especially to controls for a motor used to drive a spindle of a dental hand piece.

Dental hand pieces, as made heretofore, are driven by small electrical motors which drive some type of a flexible belt that connects to and drives a pulley carried by the spindle of the dental hand piece. The speed of the electric motor is controlled and varied, as desired, :by the operator through a control box positioned on the floor adjacent the dental chair. The control box usually had a pedal on it operable by foot for putting resistance in or taking it out of the motors circuit to control the speed of drive of the hand piece. Furthermore, the control could be used to stop, or reverse the motor when desired.

If the dentist is considerate of his patients welfare, as they substantially all are, the dentist must stand on one leg and keep the foot of the other leg constantly engaged with the speed controller. This tensed operating condition is due to the fact that it may be necessary to shut on or change the speed of the drill spindle rapidly should the drill slip or come loose in any way, or should the drill conditions change. It especially is necessary to shut off the spindle rapidly when an abrasive disc is being used on the spindle as such discs sometimes work free of the spindle. Hence, it is obvious that the spindle should be stopped rapidly to prevent a rapidly rotating disc from being thrown oii the drill spindle into the patients mouth. In all events, the foot controller causes bad Operating conditions for dentists since they cannot even stand with their weight evenly divided on two feet and still operate the controller, since frequent drill speed changes are usually required.

A further disadvantage of the foot control for a dental drill spindle is that the control is remote from the scene of drilling. Thus, every time the dentist wants to locate the speed controller, should he not have his foot in engagement with such control, the dentist must withdraw the drill and mirror or any other implement in the patients mouth at that time and take a step or two backwards, or to the side and look around in order to locate the controller. Then, too, the control is bulky, does not fit neatly in a dental ofiice, and, in general, is not as easily operable as a dentists drill control should be.

Efforts have been made to eliminate the foot control for the drive of a dental hand piece, and switches have been provided on the hand piece itself to connect to a remote motor control for varying the flexible drive of the hand piece spindle. Such controls have been relatively bulky and have not been satisfactor for that reason and because they have transmitted relatively high voltages and heavy currents which necessitate use of relatively large, heavy conductors leading to the hand piece. This obviously interferes with the required flexibility of the hand piece and some attempts also have been made to mount an electric motor in a trunnion member so that it would be directly connected to the shaft of a dental hand piece, but such constructions likewise have not provided the required lightness, flexibility and ease of control of the hand piece that is required.

The general object of this invention is to overcome the foregoing, and other objections to and dis-advantages of prior types of dental hand piece spindle controls, and to provide a control for the drive of a dental hand piece spindle, which control is characterized by its availability to the hand piece operator and its ready and easy functionability.

Another object of the invention is to provide a motor controller having a minimum of wires connected thereto and a minimum of current flowing therethrough.

A further object of the invention is to provide a remote control for an electric motor, which control has only a fraction of the motor current flowing therethrough, and which completely controls the operation of the motor.

Another object of the invention is to provide a very compact control for a small electric motor, which control has relatively low currents and voltages in relation to those of the motor circuit.

A further object of the invention is to provide an inexpensive, uncomplicated, improved control for the motor associated with a dental hand piece, which control can be operated by means on a hand tool without impairing the ready maneuverability thereof.

Another object of the invention is to permit a dentist to change, readily, the speed of operation of a hand piece spindle, to reverse the spindle, or to stop it.

The foregoing and other objects and advantages of the invention will be made apparent as the specification proceeds.

Attention now is directed to the accompanying drawings, wherein:

Fig. 1 is an elevation of a dental hand piece assembly embodying the principles of my invention;

Fig. 2 is an enlarged top plan of the switch of Fig. 1;

gaged with a spindle l2 journalled in the hous Suitable flexible.

ing formed by the hand piece. means (not shown) connect to and drive the pulley l l. A primary feature of the invention is that a small controller box it is carried by the.

hand piece l and is removably'secured-thereto,

as by screws IA. The controller box 13 has a. push button l extending therefrom and itrbears. against and is suitably secured to the upper of two resiliently mounted contact arms ldand l 'lpositioned by and extending from a bracket a secured to an insulator, or base member 20 within" the box I3. Contacts IS-and l9 may be secured to the adjacent surfaces of the arms It and H, respectively, whileconductors 2i and 22connect tothe-contact arms HS and H, respectively, so that a 'circuit iscompleted therethrough when/the push-button [5- is pressed in substantially flush with the'outer surface of the controller box. This circuit isused to start and stop the motor that drives the spindle i2, as explained more fully hereinafter.

A secondcircuit is controlled by the controller box l3-so -that a conductor 23 leads to the con.- troller-box- 13: with the conductor 23 connecting to the-one end of a suitable variable resistor '24, which may have a resistance of approximately .1 megohrn; -The resistor 2-4, in this instance,..is shownas-comprising an insulated wire 25 that is. coiled-around a non-conductive core 25, .one coil thick-, alon the length thereof. The assembly then has-a slider 2'? engaged with the upper side' of a metal strip'28 for sliding movement therealong. The insulationon the wire of coil 25 1s removed on the top side of the coil 25 so that metalstr-ip -28-may make electrical contact with coil 25immediately beneath the slider 21'. The metal'strip 28; which extends the length of the core 26, is secured to one end of the non-conductive core '26"by--'a conductive pin 29. The conductor 23- connects to the end of the pin '29 and one end of the Wire 25 also is suitably secured thereto-'while-the opposite end of the wire 25 connects to the conductor 2i. Thus, the slider 21 can be slid along the metal strip 28 to press againstyor'contact the uninsulated portions of the Wire 25 to'short out a part of such resistor through-the strip 28. The conductors 2i and 23, leading from the variable resistance, are connectedgto the motor circuit, as explained hereinafter; to control the speed of the drive of the spindle 121'.

To effect reversal of drive of the motor driving the spindle l2, the contactor'i'l carries a spring contact bar 3! on its end adjacent the pin 29 and it 'is adapted to bear on spaced contact fingers 32 and 33 when the contactor 21 is moved to its extreme position remote from the startstop button l5. The common conductor 2| also connects to the contact finger 32 whilea conductor 34 connects to the contact finger 33 and such conductors 2i and as are connectedto a suitable means for effecting reversal of the motor driving the spindle i2, as explained more fully hereinafter.

Referringnow to Fig. 4, power is supplied for driving the spindle l2 by suitable power supply leads 35 and 36 that connect to the primary era '4 transformer 31. One coil 38 of the secondary of the transformer 3'! has a lead 35 extending therefrom which connects through a series field ii and reversible switch 42 to an electric motor The motor 43 usually is of the universal type and has only a fractional horsepower output. A lead 'M connects the other side of the motor 43 to the plate, or "anode 45 of an electronic tube 4?,- that may be of the type known as Thyratrons. A filament 41 of the tube 46 connects by leads 68 and 49 to a small secondary coil 5! of the transformer 31 and the filament ii serves as a cathode for transmittal of motor current therethrough. A lead 52 connects themidepoint of the coil Si to the lowersection of the coil 33 so that the motor circuit is thereby completed. A switch 53 be-provided-inthe lead 52 to open and close the motor .circuit and thereby start or stop the motor 43, which is the motordriving the pulle H through flexible connectin means (not shown).

The conductor 2 i, that extendsto the'controller box 13; connects to the conductor 52 whilethe other lead 23 of the variable resistance Tia-icon;- nects-to one plate of a small. condenser 5d of about 225-microfarad capacity. The other. plate of condenser E l thenconnects to the lower end of the coil 38 of the transformershthereby completing' the primary phase-shifting circuit. The junction of the lead 23- with condenserv 5 conneotstc' one end of the resistor 55,4118 other end of which connects to the grid llfiofitube 45, thus connectingthe phase-shifted voltage from the primaryphase shiiting circuit to thetcontrol ale:- ment'in the motor current-controlling tube 48;:by means of resistance 55 whose-primary. function is to limit grid-filament current to so low. avalue that damagecannot occur to the grid itself i The phase of any 'almernating voltageimpressed on the:

controlgrid 56 due to thecurrent'in .the circuit of-thecoil38;conductors21, 23 and 52,.andthe condenser may be varied .by changing the =setting of'the variable resistor 24; Thus;v the motor current flowing through the Thyratron. tube 45.

can be'co'ntl'olled; since the tube will conductzonly.

portionsof alternate half cycles of the alternating.

current impressed on it and-the phase oi the grid voltage can be adjustedxto control. the time of.

starting conduction within each half cycle, the

end of the conducting periodsialways occurring.

at approximately the end of the half cycle. Control of the motor current efiects the desired control of the speed of the motor 43.

An important feature of the invention is: the control of the motor 43 without the use-of high voltages or heavy currents, which would l'lECBSn sitate' use of'hea'vy conductors, so. that light, flexible controls can be providedinthehandcone trollerwhich still would be efiective. incontrolling the motor circuit.- To this end, the conductor 22' from the startand stop switch. contactrl] leads=to -a contact 57 of a'two position. relay 58 of'a conventional design and having. two operative coils '59-and 6|. The relay 58 is held in a given positionb'y suitabledevlces; such as.

springs- .(not shown). The relay. 58 .controls. a rod or solenoid 62 which'connects to theswitch 53 and to "a switch 63 that may be associated with the relay; Hence, moving the button 25 to close the contacts l6 and l'l-energizes the coil 6| which is connected-to a lead 64 that .in turn connects to the lower portion of the secondary -coil 38. Such movement of'the solenoid 62 opens the switch-53 and closes the-switch 83 ona conductor- 65 which connects through the relay coil 59 to the lead 64-wliereby 'again-closing the contacts I8 and I9 momentarily will energize the coil 59 and close the switch 53 thereby resetting the relay 58 in its run position. Thus, the relay 58, which will operate on a low voltage such as 4 volts, can be used to start or stop the motor 43 which might have, for example, 220 volts impressed on it.

Dentists frequently reverse the direction of rotation of their drill spindles and another salient feature of the invention is that the lead 34 from the reversing switch connector 3| of the controller box connects to a contact 66 of a reversing relay 6?. The contact has a switch 68 associated with it and the switch 68 is adapted to connect to a lead 69 that connects through a relay operating coil H to the lead 64. The switch 68 is controlled by a solenoid 12, or other means that is positioned by the relay 61, and in its reverse position connects toa lead 13 that connects through a coil "to the lead 64. Hence, in either of its positions, the relay 61 has an operative coil ready to function the relay upon closing the contact 3| on-the contact fingers 32 and 33 with the relay being retained in a given position by any conventional means. The solenoid I2 is secured to movable switches 13a and Ma in the reverse switch 42 which switches eifect the reversal of flow of current through the motor 43 through bifurcated end leads and 16. Again the motor control is efiected from the controller box IS with only a low voltage, say 4 volts, being impressed on the reversal means of the control. It should be observed that reversal of the motor only can occur when the contact 21 is at its extreme position with all of the resistance in the controller box circuit which condition causes the motor 43 to run at its slowest speed.

As a further feature, the start and stop relay 58 may also set up some dynamic braking action in the motor 43 to stop it rapidly. Thus, switches 57 and 18 may be secured to the solenoid 62 and they close circuits through suitable resistances i9 and 8i. The resistance 19 is connected in shunt with the motor 43 by a lead 82 whereas the resistance BI and switch 11 are located in a conductor 83 that extends between the lead 52 and the junction of the series field 4| and the reversing switch 13a to keep current flowing in the field 4! to aid in effecting dynamic braking of the motor.

While the controller box [3 is shown, for convenience, as being secured to a dental hand piece, it will be understood that the controller box is may be mounted on other dental hand tools, such as a mouth lamp, without losing the benefits of the invention.

Naturally, the resistance 24, condenser 54 and other variable devices and voltages of the circuit of the invention are chosen so as to give the desired operation under the probable operating conditions in a small motor circuit. The controller or switch box I3 is of minimum size, being about 1 long, wide and high in one instance, and is of maximum flexibility due to the small number and size of the conductors leadin to it. However, it provides a complete controller box for a controller slave unit, including a dental motor. The controller box can be removed from the hand piece ID, if desired, when the hand piece is to be sterilized but its construction is such that it can stand sterilization conditions.

To simplify changes of the hand piece, and its sterilization, it might be desirable to have the conductors connecting to the hand piece controller to be grouped into one connector pluglnot shown) that would easily be engaged with, or disengaged from the controller box l3. 7

In some instances, it may be desirable to use a shunt motor in place of the series motor shown but it will be apparent that the principles of our invention apply equally well to any type of small D. C. or universal motor. The shunt field, with a small resistance and rectifier in series with it, could be connected across the upper part of the coil 38 and the resistance 8| and its associated circuit could be omitted, when a shunt motor is used.

In the controller box i3, portions of the wires extending through the box are not shown and they may be embedded in the base member or be otherwise conventionally led through the box to contact blocks 2% provided at the connection end of the box.

From the foregoing, it will be seen that a compact, easily operated motor control is provided for use in controlling small dental motors. This control is adapted for positioning for ready use by a dentist and overcomes the difiiculties attendant use of previous types of controls so that the objects of the invention are achieved.

While in accord with the patent statutes we have specifically illustrated and described one embodiment of our invention, it should be understood that the invention is not limited thereto or thereby but that the scope of the invention is defined in the appended claims.

We claim:

1. A control member for an electric motor comprising a base; a pair of resilient contact arms mounted in spaced horizontal relation on said base but adapted to be moved to temporarily contacting relation; a switch button carried on the upper surface of the upper of said contact arms for moving such arm down against the other of said arms; an elongated resistor unit carried by said base, said unit including a flat insulator core element, an insulated wire wound around the core element and having the insulation removed longitudinally at the center of the upper fiat side, a contactor slidably engaged with the core element and bearing on the uninsulated parts of the wire, and a flat metal strip associated with the core element intermediate it and the contactor for shorting out part of the resistor; a pair of contact fingers carried by said at one end of said resistor unit; a spring contact carried by the contactor of said resistance unit and adapted to close a contact through 55 said contact fin ers when the contactor is at its extremity of movement with none of the wire of said resistance unit shorted out of its circuit; and conductors connecting to said contact arms, said contact fingers, and said resistance unit, one of said conductors being a common connection to the three elements of the control member.

2. A control member for an electric motor comprising a base; a pair of resilient contact arms mounted in spaced horizontal relation on said base but adapted to be moved to contacting relations; a switch button carried on one of said contact arms for moving it against the other 01' said arms; an elongated variable resistor unit carried by said base and having a movable element; a pair of contact fingers carried by said base at one end of said resistor unit; a contact element carried by the movable element of said resistance unit and adapted to contact said contact fingers and close a circuit therethrough 75 when the element is at its extremity of movement with none of said resistance unit shorted out of its circuit; and conductors connecting to said contact arms, said contact fingers, and said resistance unit, one of said conductors being a common connection to the three elements of the control member.

3, A rheostat and reversing switch comprising a frame, an elongated resistor unit carried by said frame and having a slider thereon, a resilient contact strip secured to said slider and extending from one portion thereof, said contact strip being separate from the circuit of said resistor unit, and a pair of spaced contacts carried by said frame and protruding therefrom adjacent said resistor unit, said contact strip contacting said contacts and closing a circuit between said contacts when said slider is at a predetermined position on said resistance unit.

4. A rheostat and reversing switch comprising a frame, an elongated resistor unit carried by said frame and having a slider thereon, a contactor secured to said slider and extending substantially axially from one portion thereof, and a pair of spaced contacts carried by said frame adjacent one end of said resistor unit, said contactor being adapted to strike said contacts and close a circuit between said contacts when said slider is at a predetermined position on said resistance unit.

JEAN C. BARNES. IRA. B. PENNIMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

